Retaining plate for a vacuum-cleaner filter bag

ABSTRACT

The invention comprises a retaining plate (1), comprising a first plate (2) and a second plate (3) arranged in a first plane, and a third plate (8) arranged in a second plane which runs in parallel to the first plane, the third plate (8) having a lower flexural stiffness than the first plate (2) and the second plate (3), wherein the first plate (2) and the second plate (3) are interconnected by means of the third plate (8) such that a hinge is formed between the first plate (2) and the second plate (3) about the hinge axis (A) of which the first plate (2) and/or the second plate (3) can be bent together with the respective part of the third plate (8) connected thereto.

The invention relates to a retaining plate for a vacuum-cleaner filterbag and to a vacuum-cleaner filter bag having such a retaining plate.

Many solutions are known to fix vacuum-cleaner filter bags in theinstallation space of the vacuum cleaner. In most cases, so-calledretaining plates are used, that means flat components which areconnected with the bag wall of the vacuum-cleaner filter bag and have apassage opening overlapping the admission opening of the bag wall. Theretaining plate is pushed into a corresponding mounting in the vacuumcleaner before the latter is switched on, so that it is arranged in acertain position. When the vacuum cleaner is subsequently closed, aconnecting piece of the vacuum cleaner engages with the passage openingof the retaining plate so that the air to be filtered can flow into thevacuum-cleaner filter bag. Moreover, solutions are known which do notuse any retaining plate but are based, for example, on connecting pieceswhich are put onto corresponding counterparts in the installation spaceof the vacuum cleaner, as is disclosed, for example, in U.S. Pat. No.2,068,332.

Due to limitations with respect to the installation space, retainingplates which include flexible regions were suggested, so that theactually flat components can also be pushed into bent guides. By this, abetter adaptation to the installation space is to be permitted. Examplesof such retaining plates are known from WO 2017/194081 A1 and WO2017/196211 A1. One suggested solution uses integral hinges in order todesign one region of the retaining plate flexibly. However, this caneasily lead to component failures due to integral hinges which cannot besufficiently loaded mechanically. In particular, the integral hinges canbe even more weakened by the use of recycled plastics, such as recycledpolypropylene, rPP. For ecological deliberations, the use of recycledplastics is becoming increasingly desirable. Moreover, the formation ofthe integral hinges by injection molding is also cumbersome.

It is therefore the object of the invention to provide an improvedretaining plate for a vacuum-cleaner filter bag which is in particularmore reliably applied and easier to manufacture.

This object is achieved by a vacuum-cleaner filter bag according toclaim 1. Particularly advantageous developments can be found in thesubclaims.

That means, the invention provides a retaining plate comprising a firstplate and a second plate arranged in a first plane, and a third platearranged in a second plane which runs parallel to the first plane, thethird plate having lower flexural stiffness than the first plate and thesecond plate, the first plate and the second plate being interconnectedby means of the third plate such that a hinge is formed between thefirst plate and the second plate about the hinge axis of which the firstplate and/or the second plate can be bent together with the respectivepart of the third plate connected thereto.

By the hinge not being formed by a weakening line in the material as iscommon in prior art, but by a combination of the three plates, theretaining plate, in particular the hinge, can be designed to have a morereliable function and to be more flexible in view of the properties tobe achieved. For example, plates that have been produced with differentmanufacturing processes can be also combined. Thus, one or more plateshaving a particularly sophisticated geometry can be molded parts. Forsimpler structures, the thermoforming method is also suited. It is thusalso possible to combine various materials. For example, the third platewhich is bent in use can also comprise a material which is particularlysuited for this, such as for example a thermoplastic elastomer, TPE, orconsist thereof. It is thereby then also possible to realize a sealintegrally around the vacuum-cleaner connecting piece through the thirdTPE plate.

The term “plate” here refers to a flat component, that means a componentwhose extension in one plane (plate width and plate length) is clearlylarger than its extension perpendicular to this plane (plate thickness).

The flexural stiffness describes the resistance of the plate againstelastic deformation by a bending moment and is defined in the mannerknown to the person skilled in the art.

The third plate can have a one-piece design or be made of a plurality ofinterconnected parts. However, the third plate is in any case designedsuch that it connects the first plate with the second plate.

The retaining plate can in particular comprise one or more plastics orconsist of one or more plastics. In particular, recycled plastics canalso be employed, such as recycled polypropylene, rPP, and/or recycledpolyethylene terephthalate, rPET. The recycled plastic material can inparticular be used for the first plate and the second plate. The thirdplate can then also comprise new plastic material (virgin material) orconsist thereof.

The retaining plate can be formed of a combination of molded parts or acombination of parts produced by thermoforming. The retaining plate canalso comprise elements partially made by injection-molding and partiallyby thermoforming.

The first plate can in particular be connected with the second plateonly via the third plate. In other words, the first plate and the secondplate can be completely separate components. However, this does notexclude that a physical contact between the first plate and the secondplate is present or can be present in certain positions. Here, thecontact surface can also be selectively formed, for example drawnupwards at the edge, to achieve a larger contact surface and/or topermit a movement only in one direction and/or to restrict the possiblebending angle.

The hinge axis can in particular extent in parallel to the parting linebetween the first plate and the second plate. The hinge axis then alsolies in a plane parallel to the first and second planes, in particularin the second plane.

The third plate can in particular be thinner than the first plate and/orthe second plate. The thickness is here determined perpendicular to thefirst and second planes. With a non-constant thickness, the averagethickness can be taken as a quantity. By the smaller thickness, a higherflexibility, that means a lower flexural stiffness, can be achieved in asimple manner, in particular also if the same material is used for allplates. For example, the third plate can have a thickness of 0.05 to 1.0mm, while the first plate and the second plate each have a thickness of1.0 to 3.0 mm.

The third plate can, as an alternative or additionally, be made of amaterial different from that of the first plate and/or the second plate,the material of the third plate having a lower elastic modulus than thematerial of the first plate and/or the second plate.

The first plate and the second plate can be glued, welded, or positivelyconnected to the third plate. The connection can be designed to bedetachable nondestructively or not nondestructively. As a positiveconnection, a rivet connection is in particular possible.

In the first plate, a passage opening can be arranged which inparticular overlaps with a passage opening in the third plate. Thepassage opening or openings form the filling hole when the retainingplate is connected with a vacuum-cleaner filter bag.

The retaining plate can moreover comprise a sealing lip surrounding thepassage opening. The sealing lip can comprise or consist of athermoplastic elastomer, for example based on polypropylene. The sealinglip is to prevent or restrict dust from leaking from the vacuum-cleanerfilter bag by sealing the region between the inner edge of the passageopening and the outside of a connecting piece of the vacuum cleaner. Itis in particular possible to form the sealing lip by parts of the thirdplate if it comprises or consists of a thermoplastic elastomer, TPE, bythe passage opening in the third plate having a smaller diameter thanthe passage opening in the first plate.

In the second plate, one or more positioning openings can be providedfor positioning and/or fixing it in a retaining plate mounting. In thethird plate, correspondingly overlapping positioning openings can beprovided so that the positioning openings are present in the retainingplate in the form of passage openings. However, the positioning openingscan also be designed as blind holes. In operation, positioning elementsof the retaining plate mounting of the vacuum cleaner can engage withthe positioning openings and thereby position and/or fix the retainingplate.

The invention moreover provides a vacuum-cleaner filter bag comprising abag wall and a retaining plate described above and connected therewith.

The bag wall is made from an air-permeable material and can be made inmultiple layers. The latter is also referred to as a laminate. Multiplelayers of the laminate, in particular each layer of the laminate, cancomprise a non-woven fabric and/or a fibrous web or consist thereof.

As a material for the bag wall, in particular for one or several layersof non-woven fabric or fibrous web, many diverse plastics can be used,for example polypropylene and/or polyester. The bag wall can alsocomprise or consist of plastic recyclates and/or recycled material fromthe manufacture of textiles (Textile Left-Over—TLO).

For many plastic recyclates, there are relevant international standards.For PET plastic recyclates, for example, DIN EN 15353:2007 is relevant.PP recyclates are characterized in DIN EN 15345:2008. For the purpose ofthe corresponding special plastic recyclates, the present patentapplication adopts the definitions of these international standards. Theplastic recyclates can be non-metallized. One example of this areplastic flakes or chips recovered from PET beverage bottles. Equally,the plastic recyclates can be metallized, e. g. if the recyclates havebeen obtained from metallic plastic foils, in particular metallized PETfoils (MPET).

Recycled polyethylene terephthalate (rPET) can be obtained, for example,from beverage bottles, in particular so-called bottle flakes, that meanspieces of ground beverage bottles.

The recycled plastics, in particular recycled PET and/or recycled PP,both in the metallized and in the non-metallized version, can be spuninto the corresponding fibers from which the corresponding staple fibersor melt-blown or spunbond non-woven fabrics can be manufactured for thepurposes of the present invention.

Recycled material from the manufacture of textiles (TLO) is inparticular generated in the processing of textile materials (inparticular textile fibers and filaments, and linear, planiform, andspatial textile fabrics manufactured therewith), such as, for example,the manufacture (comprising carding, spinning, cutting, and drying) orthe recycling of textile materials. These pulverized and/or fibrousmaterials are waste materials which can deposit on the machines orfilter materials used for processing the textiles. The dusts (powders)or fibers are normally disposed of and thermally utilized.

So, the pulverized and/or fibrous recycled material is, for example,production waste; this in particular applies to material generatedduring the carding, spinning, cutting, or drying of textile materials asa waste product. This is also referred to as “pre-consumer waste”.

Also in the recycling of textile materials, i. e. the processing (forexample crushing) of used textile materials or textiles (for example oldclothes), pulverized and/or fibrous recycled material is formed, this isreferred to as “post-consumer waste”.

So, the recycled material from the manufacture of textiles, TLO, can inparticular comprise fibers and/or filaments which have been obtainedfrom waste materials from the textile and clothing industry, frompost-consumer waste (textiles and the like), and/or from products thathave been collected for recycling.

In the sense of the present invention, a non-woven fabric designates anentangled mesh that has undergone a solidification step so that it hassufficient strength to be wound off or up from or onto rolls, forexample by machines (i. e. on an industrial scale). The minimum webtension required for winding up is 0.044 N/mm. The web tension shouldnot be higher than 10% to 25% of the minimum maximum tensile force(according to DIN EN 29073-3:1992-08) of the material to be wound up.This results in a minimum maximum tensile force for a material to bewound up of 8.8 N per 5 cm of the strip width.

A fibrous web, briefly only referred to as “web”, corresponds to anentangled mesh which, however, has not undergone a solidification step,so that in contrast to a non-woven fabric, such an entangled mesh doesnot have sufficient strength to be wound off or up, respectively, intoor from rolls, for example by machines.

The term non-woven fabric (“non-woven”) is used in other words accordingto the definition of ISO Standard ISO9092:1988 or CEM Standard EN29092.Details on the use of the definitions and/or methods described hereincan also be taken from the standard work “Vliesstoffe”, W. Albrecht, H.Fuchs, W. Kittelmann, Wiley-VCH, 2000.

The non-woven fabric layers of the bag wall can in particular comprise astaple fiber non-woven fabric and or an extrusion non-woven fabric. Inparticular, spun-bond nonwovens (briefly also “spun-bond web” orspundbond”), and/or melt-blown non-woven fabric can be used.

One or several layers of the bag wall can comprise a carded material. Asa bonding step, mechanical methods (e. g. needling) as well as thermalmethods (e. g. calendaring) are possible. Equally, the use of bindingfibers or adhesives, such as a latex adhesive, is possible. Airlaidmaterials are also possible.

The non-woven fabric of one or several layers of the bag wall cancomprise bicomponent fibers. Bicomponent fibers (bico fibers) can beformed of a core and an envelope enclosing the core. Apart fromcore/envelope bicomponent fibers, the other common variations ofbicomponent fibers, e. g. side-by-side, can be employed.

The bicomponent fibers can be present as staple fibers or be formed asfilaments in an extrusion non-woven fabric (for example, melt-blownnon-woven fabric).

Correspondingly non-solidified fibrous webs are also conceivable, asmentioned.

The non-woven fabric of one or several layers of the bag wall canmoreover include a microcreping (Micrex).

The bag wall can also comprise an odor absorbent.

The bag wall can in particular comprise a capacity layer. A capacitylayer offers a high resistance against shock loads and permits filteringof large particles of dirt, filtering a significant proportion of smallparticles of dirt, and storing or retaining high amounts of particles,wherein the air is allowed to easily flow through, thus resulting in alow pressure drop with a high particle load.

The bag wall can also comprise a fine filter layer. A fine filter layerserves to increase the filtration performance of the multi-layer filtermaterial by capturing particles which penetrate, for example, thecapacity layer. To further increase the separation performance, the finefilter layer can be preferably charged electrostatically (e. g. bycorona discharge or hydro-charging), to in particular increase theseparation of particulate matter.

The fine filter layer can be adjacent to the capacity layer inparticular towards the outside of the bag wall.

A support layer can also be adjacent to the fine filter layer. A supportlayer (sometimes also referred to as “reinforcement layer”) is here alayer that imparts the required mechanical strength to the multi-layerbond of the filter material. The support layer can in particular be anopen, porous non-woven fabric with a light grammage. The support layercan in particular be a spun-bond web.

However, it is also possible to employ a single-layer filter materialfor the bag wall. In this case, it can in particular be a melt-blownnon-woven fabric. A suited material for such a single-layer bag wall isknown, for example, from EP 2 311 360 B1.

The retaining plate can comprise one or several ones of theabove-described features.

The bag wall can in particular be welded to the third plate, the thirdplate comprising a plastic which is compatible with the plastic materialof the outermost layer of the bag wall to which the third plate iswelded. In other words, the material of the third plate can be selectedsuch that it can be welded to the bag wall as firmly as possible.

For good welding results, it is necessary for the materials to beconnected to be preferably matched both with respect to their meltingpoints and their chemical natures (amorphous/semicrystalline). This canbe achieved if compatible materials are used. It is also conceivable touse the same materials for the outermost layer of the bag wall, to whichthe third plate is welded, and for the third plate.

However, it is also possible for the bag wall to be connected with thefirst plate or the second plate. In this case, the respective plate cancomprise a plastic compatible with the plastic material of the outermostlayer of the bag wall to which the respective plate is welded.

The invention moreover provides a system comprising a vacuum-cleanerfilter bag described above and a mounting for the retaining plate in avacuum-cleaner housing, wherein the mounting is designed such that thefirst plate and/or the second plate and the respective part of the thirdplate connected thereto are bent about the hinge axis in the operatingposition with respect to the first and second planes. The operatingposition is defined here as the position in which the retaining plate isarranged in the operation of the vacuum cleaner.

The vacuum-cleaner filter bag can comprise one or several ones of theabove-described features.

The mounting can in particular have a guide along which the retainingplate can be inserted into the mounting. This guide can comprise astraight and a bent section. By the bent section, the bending about thehinge axis can be caused.

The mounting can in particular be designed as described in WO2018/095519 A1.

Further features and advantages of the invention will be described belowwith reference to the exemplary figures. In the drawings:

FIG. 1 shows a plan view onto an exemplary retaining plate;

FIG. 2 shows a section through an exemplary retaining plate;

FIG. 3 shows a side view of an exemplary retaining plate in a firstposition;

FIG. 4 shows a side view of an exemplary retaining plate in a secondposition; and

FIG. 5 shows a plan view onto an exemplary vacuum-cleaner filter bag.

FIG. 1 shows a plan view onto an exemplary retaining plate 1, comprisinga first plate 2 and a second plate 3 which are embodied as completelyseparate components. In this example, the plates 2, 3 are spaced apartby a gap 7. It would also be conceivable for the plates 2, 3 to toucheach other in this arrangement as long as they remain separatecomponents. The first plate 2 and the second plate 3 are only connectedby a third plate which cannot be seen in FIG. 1 and which is arranged ina plane parallel to the plane of the first plate 2 and the second plate3 and is in particular also provided in the region under the gap 7.

FIG. 2 shows a section through the exemplary retaining plate 1. Thethird plate 8 is arranged under the first plate 2, the second plate 3,and in particular under the gap 7, so that the third plate 8 connectsthe plates 2, 3. The third plate 8 is arranged on the side of theretaining plate 1 that is provided for the connection with the bag wallof a vacuum-cleaner filter bag.

The third plate 8 moreover has a lower flexural stiffness than the firstplate 2 and/or the second plate 3. In this example, this is achieved inthat the third plate 8 is thinner both than the first plate and thesecond plate 3. As an alternative or in addition, the third plate 8 canbe made of a material different from that of the first plate 2 and/orthe second plate 3, wherein the material of the third plate has a lowerelastic modulus than the material of the first plate 2 and/or the secondplate 3.

By the higher flexibility of the third plate and the reduced thicknessof the retaining plate 1 in the region of the gap 7 between the plates2, 3, a hinge is formed. The hinge axis A is indicated in FIG. 1 by adashed line. The second plate 3 can be bent or pivoted about this hingeaxis A with respect to the first plate 2 together with the part of thethird plate 8 connected thereto. This is represented in FIGS. 3 and 4 .In FIG. 3 , all plates 2, 3, 8 are completely located in two parallelplanes, while in FIG. 4 , the second plate 3 and the part of the thirdplate 8 connected thereto are bent about the hinge axis Aperpendicularly to the planes of FIG. 3 . Thereby, the retaining plate 1can also be introduced into mountings which have a bent guide andthereby require a retaining plate with flexible regions.

As is shown in FIGS. 1 and 2 , in the first plate 2, a passage opening 4is formed which also extends, as is shown in FIG. 2 , through the thirdplate 8. Thereby, an admission opening is formed together with a passageopening of the bag wall of a vacuum-cleaner filter bag. However, it isalso conceivable that the third plate 8 does not extend over thecomplete bottom side of the first plate 1 and thus does not overlap thepassage opening 4 in the first plate 2. The admission opening is thenformed only by the passage opening 4 in the first plate 2 together withthe passage opening of the bag wall.

The retaining plate 1 has a sealing lip 10 of a thermoplastic elastomer,TPE, in a manner known per se which is molded to the edge of the passageopening 4 of the first plate 2 in this example. However, it is alsopossible to form the sealing lip 10 by the third plate 8 if it comprisesor consists of a thermoplastic elastomer, TPE, by the passage opening inthe third plate 8 having a smaller diameter than the passage opening 4in the first plate 2. According to further alternatives, the sealing lip10 can also be glued or welded onto the first plate 2 from above or fromthe bottom. “Above” here refers to the side facing away from the thirdplate 8, and “bottom” to the side facing the third plate 8.

One can also see in FIG. 1 two positioning openings 5, 6 in the secondplate 3 for positioning and/or fastening it in a retaining platemounting. The positioning openings 5, 6 can also be provided as passageholes in the third plate 8. In operation, positioning elements of theretaining plate mounting of the vacuum cleaner can engage with thepositioning openings 5, 6 and thereby position and/or fix the retainingplate 1.

In FIG. 5 , the retaining plate 1 is connected to a bag wall 9 of avacuum-cleaner filter bag. The bag wall 9 can in particular be welded tothe third plate 8, the third plate 8 comprising a plastic which iscompatible with the plastic material of the outermost layer of the bagwall 9 to which the third plate 8 is welded. Thereby, the strength ofthe welded joint between the retaining plate 1 and the bag wall 9 can beimproved.

The bag wall 9 comprises a plurality of non-woven fabric layers or aplurality of non-woven fabric and fibrous web layers which overlap eachother from the bag's interior to the bag's exterior. The non-wovenfabric or fibrous web layers can be loosely lie one upon the other or beconnected to each other. The connections can be accomplished across thesurface (e. g. via spray adhesives), or punctually (e. g. via acalendaring pattern).

The individual layers can in particular comprise different plasticmaterials, both among each other and/or within one respective layer.

The exemplary vacuum-cleaner filter bag of FIG. 5 is a so-called flatbag wherein the bag wall 9 comprises an upper side and a bottom sidewhich are connected to each other by a surrounding weld seam. Both theupper side and the bottom side of the flat bag comprise, as mentionedabove, a plurality of filter material layers, in particular a pluralityof non-woven fabric layers or a plurality of non-woven fabric andfibrous web layers. Both the upper side and the bottom side can inparticular be formed of a laminate of a plurality of non-woven fabriclayers. However, the invention is not limited to flat bags but can alsobe applied, for example, for gusset bags or pad bottom bags.

Advantageously, the retaining plate 1 in this example comprises arecycled plastic material, for example, recycled polypropylene (rPP) orrecycled polyethylene terephthalate (rPET).

It will be understood that features mentioned in the above-describedembodiments are not restricted to these special combinations and arealso possible in any other combinations. It will be furthermoreunderstood that geometries shown in the figures are only given by way ofexample and are also possible in any other designs.

1. A retaining plate, comprising a first plate and a second platearranged in a first plane, and a third plate arranged in a second planewhich runs in parallel to the first plane, the third plate having alower flexural stiffness than the first plate and the second plate,wherein the first plate and the second plate are interconnected by meansof the third plate such that a hinge is formed between the first plateand the second plate about a hinge axis (A) of which the first plateand/or the second plate can be bent together with a respective part ofthe third plate connected thereto.
 2. The retaining plate according toclaim 1, wherein the third plate is designed to be thinner than thefirst plate and/or the second plate.
 3. The retaining plate according toclaim 1, wherein the third plate is made of a material different fromthat of the first plate and/or the second plate, wherein the material ofthe third plate has a lower elastic modulus than the material of thefirst plate and/or the second plate.
 4. The retaining plate according toclaim 1, wherein the first plate and the second plate are glued, welded,or positively connected to the third plate.
 5. The retaining plateaccording to claim 1, wherein in the first plate, a passage opening isarranged which in particular overlaps with a passage opening in thethird plate.
 6. The retaining plate according to claim 1, wherein in thesecond plate, one or more positioning openings are provided forpositioning and/or fastening it in a retaining plate mounting.
 7. Avacuum-cleaner filter bag, comprising: a bag wall and a retaining plateconnected thereto; wherein the retaining plate comprises a first plateand a second plate arranged in a first plane, and a third plate arrangedin a second plane which runs in parallel to the first plane, the thirdplate having a lower flexural stiffness than the first plate and thesecond plate; and wherein the first plate and the second plate areinterconnected by means of the third plate such that a hinge is formedbetween the first plate and the second plate about a hinge axis (A) ofwhich the first plate and/or the second plate can be bent together witha respective part of the third plate connected thereto.
 8. Thevacuum-cleaner filter bag according to claim 7, wherein the bag wall iswelded to the third plate, and wherein the third plate comprises aplastic which is compatible with a plastic material of an outermostlayer of the bag wall to which the third plate is welded.
 9. A system,the system comprising: a vacuum-cleaner filter bag, the vacuum-cleanerfilter bag comprising: a bag wall and a retaining plate connectedthereto; and wherein the retaining plate comprises a first plate and asecond plate arranged in a first plane, and a third plate arranged in asecond plane which runs in parallel to the first plane, the third platehaving a lower flexural stiffness than the first plate and the secondplate, and wherein the first plate and the second plate areinterconnected by means of the third plate such that a hinge is formedbetween the first plate and the second plate about a hinge axis (A) ofwhich the first plate and/or the second plate can be bent together witha respective part of the third plate connected thereto; and a mountingfor the retaining plate in a vacuum-cleaner housing, wherein themounting is designed such that the first plate and/or the second plateand the respective part of the third plate connected thereto are bentabout the hinge axis (A) in an operating position with respect to thefirst and second planes.
 10. The retaining plate according to claim 2,wherein the third plate is made of a material different from that of thefirst plate and/or the second plate, and wherein the material of thethird plate has a lower elastic modulus than the material of the firstplate and/or the second plate.
 11. The retaining plate according toclaim 10, wherein the first plate and the second plate are glued,welded, or positively connected to the third plate.
 12. Thevacuum-cleaner filter bag according to claim 8, wherein the third plateis designed to be thinner than the first plate and/or the second plate.13. The vacuum-cleaner filter bag according to claim 8, wherein thethird plate is made of a material different from that of the first plateand/or the second plate, and wherein the material of the third plate hasa lower elastic modulus than the material of the first plate and/or thesecond plate.
 14. The vacuum-cleaner filter bag according to claim 8,wherein the first plate and the second plate are glued, welded, orpositively connected to the third plate.
 15. The vacuum-cleaner filterbag according to claim 8, wherein in the first plate, a passage openingis arranged which in particular overlaps with a passage opening in thethird plate.
 16. The system according to claim 9, wherein the thirdplate is designed to be thinner than the first plate and/or the secondplate.
 17. The system according to claim 9, wherein the third plate ismade of a material different from that of the first plate and/or thesecond plate, and wherein the material of the third plate has a lowerelastic modulus than the material of the first plate and/or the secondplate.
 18. The system according to claim 9, wherein the first plate andthe second plate are glued, welded, or positively connected to the thirdplate.
 19. The system according to claim 9, wherein in the first plate,a passage opening is arranged which in particular overlaps with apassage opening in the third plate.
 20. The system according to claim 9,wherein in the second plate, one or more positioning openings areprovided for positioning and/or fastening it in a retaining platemounting.